For the past twenty years, the electronic technology has been developed very fast and applied to the fields of the power, the chemical engineer, and the communication. The electronic devices are mostly operated through the converters and the interface of the power net. The conventional converter is a nonlinear circuit consisted of the diode or silicon controlled rectifier (SCR), which generates lots of current harmonic waves and zero power and thus becomes the pollution of the electronic device to contaminate the power net.
The electronic device has been one of the major sources of the harmonic waves. Currently, one of the major methods for inhibiting the harmonic waves produced by the electric device is an active method. The active method designs a new converter with high efficiency and having the characteristics of a sine input current, a low harmonic wave, and a high power factor, i.e. having the power factor correction function. Therefore, recently, the development of the power factor correction circuit has also been great and become one of the important directions for the field of the electronics study.
The technique of the single-phase power factor correction on the circuit topology and the controlling has become maturer and maturer recently. The power of the three-phase converter is relatively high, so the contamination for the power network is much higher. In the application of the three-phase input voltage, there are already lots of traditional methods for decreasing the total harmonic distortion (THD) of the input current.
First, a common method is a three-phase single-switch power factor correction circuit, which is advantageous in that the number of elements in the circuit is lower and hence the power density thereof is higher. The disadvantage of such circuit is that the three-phase input currents will affect each other, and hence the controlling effect of the THD is not good enough.
Furthermore, another common method is to combine three single-phase power factor correction circuits to control the three-phase input current. In this method, each of the three single-phase power factor correction circuits is independent, so the controlling effect of the THD is satisfactory and the efficiency thereof is higher. The disadvantage of the circuit is that the number of elements in such circuit is higher and thus the system power density thereof is lower.
Please refer to FIG. 1, which shows a circuit diagram of a conventional three-phase four-line power factor correction circuit, which is formed by three single-phase power factor correction circuits.
In the circuit, due to the existence of the middle-line N, the three single-phase power factor correction circuits won't affect each other, i.e. the three-phase voltages A, B, C are operated independently via their own modules. For the voltage of the phase A, when the voltage is positive, the diode D1 is switched on and the switch S1 is chopped. When the switch S1 is switched on, the inductance L1 stores the energy via the way: inductance L1-diode D1-switch S1-middle-line N. When the switch S1 is switched off, the inductance L1 releases the energy via the way: inductance L1-diode D1-diode D7-capacitor C1-middle-line N, and charges the capacitor C1 and adjusts the duty cycle of the switch S1 according to different requirements to make the output voltage achieve the required value.
On the other hand, when the voltage of the phase A is negative, the diode D2 is switched on and the switch S2 is chopped. When the switch S2 is switched on, the inductance L1 stores the energy via the way: middle-line N-switch S2-diode D2-inductance D2. When the switch S2 is switched off, the inductance L1 releases the energy via the way: middle-line N-capacitor C2-diode D8-diode D2-inductance L1, and charges the capacitor C2 and adjusts the duty cycle of the switch S2 appropriately to make the voltage on the capacitor C2 the required value.
As for the respective operating principles of the voltages of the phases B and C, they are the same as that of the voltage of the phase A as described above.
In such conventional circuit, the three single-phase power factor correction circuits do not affect each other, and hence the control method is simpler and the THD of the input current is lower. Besides, if one of the phase voltages fails, the others still can provide power to the load. Therefore, the circuit has the redundancy feature. However, such circuit has the following drawbacks:
(a) the utility rate of the circuit elements is low
For example, when the voltage of the phase A is positive, the switch S2 is not used. Moreover, when the voltage of the phase A is negative, the switch S1 is not used.
(b) the number of elements in the circuit is high
Because the circuit uses too many elements, the production cost therefor is getting higher directly.
In order to overcome the drawbacks in the prior art, an integrated converter having three-phase power factor correction is provided. The particular design in the present invention not only solves the problems described above, but also is easy to be implemented. Thus, the invention has the utility for the industry.